Nazila Dardmeh; Asghar Khosrowshahi; Hadi Almasi; Mohsen Zandi
Abstract
Introduction: Nanocomposites are prepared by introduction of dispersed nanoscale particles into the polymer matrix based on four methods: template synthesis (sol-gel preparation); intercalation of polymer; and in situ intercalative polymerization and last one is melt blending, the most favorable and ...
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Introduction: Nanocomposites are prepared by introduction of dispersed nanoscale particles into the polymer matrix based on four methods: template synthesis (sol-gel preparation); intercalation of polymer; and in situ intercalative polymerization and last one is melt blending, the most favorable and practical method due to its simplest, economical and environmentally friendly technic. This method involves annealing, statically or under shear, a mixture of the polymer and organically modified clay at the softening point of the polymer based on usual compounding devices, such as, extruders or mixers (Papaspyridesb 2008). PET is a semicrystalline thermoplastic polyester which has been extensively used in all sizes as a packaging material in direct contact with food, beverages and as an alternative packaging to polyvinyl chloride for edible oils (Kirwan et al. 2011). As polymeric nanocomposites are mainly used as structural materials, the layered silicate clay are preferred. The crystal lattice of 2:1 layered silicates, consists of two-dimensional layers where a central octahedral sheet of alumina is fused to two external silica tetrahedral by the tip. Montmorillonite (MMT) belongs to type 2:1 layered smectite clay which in the basic structure, the trivalent Al-cation in the octahedral layer is partially substituted by the divalent Mg-cation (Pavlidoua and Papaspyridesb 2008). As evident, MMT is greatly hydrophilic in the interlayer and incompatible with organic polymer such as PET, thus to increase compatibility of clay with polymer, inorganic inter-layer cations (Na+, K+ or Ca2+) exchanged by the cationic surfactants (e.g., quaternary ammonium salt). Modified MMT or organoclay interacts better with polymer due to its increased gallery space (Utracki et al. 2007; Parvinzadeh et al.2010). Three different types polymer/clay nanocomposites can be obtained depending on the preparation method and the nature of the components used, including polymer matrix, layered silicate and organic cation. Tactoid nanocomposites formed when stacks of modified layered silicates are retained after introduction into the polymer. Subsequently, interaction between the nanolayers and polymer is not only unsuccessful but reduces mechanical properties of composite as well. Our main objective of this research was to study the effect of the nanoclay addition on mechanical, colorimetric and transparency properties of poly (ethylene terephthalate) (PET) nanocmposite films. Materials and methods: Bottle-grade poly (ethylene terephthalate) granules with intrinsic viscosity of (IV) = 0.82 dl g-1 were provided by the Iranian Tondgooyan Petrochemical company. The organically modified montmorillonite, Cloisite 15A, was supplied by Southern Clay Products Inc. Standard of TPA was supplied from Fluka Chemical, trademarked Sigma-Aldrich Corp., Switzerland. High-pressure liquid chromatography (HPLC) grade water, aceto-nitrile, acetic acid and methanol (HPLC grade) were purchased from Merck (Darmstadt, Germany). TPA was dissolved into methanol with a slight increase in temperature. Working standard solutions were prepared on the day of use at concentrations of 0.4, 40, 100 and 1,000 ppb and calibration graphs were plotted using these concentrations of standard solutions. The PET granules and nanoclay particles were dried in an oven for 24 h at 110 and 80C before extrusion, respectively. Melt blending technique was used for preparing nanocomposite films in a co-rotating twin screw extruder ZSK 25 .The temperature profile (throat to die) was as follows: 250, 270, 275, 270, 270 and 265C with a screw speed of 250 rpm. PET granules were dry mixed with 1, 3, and 5% wt of Cloisite 15A. The total weight of material per batch was 300 g. The resulting nano-composite strand was cooled in a water bath, granulated and dried overnight in oven at 110C. A laboratory press with a temperature plates of 280C under a pressure of 5 MPa for 10 min was applied to compress specimens. Then cooled them in water and ice bath to achieve transparent films. The influence of different amount of nanoclay addition on resultant nanocmposites was studied by Fourier transform infrared spectroscopy (FT-IR) and mechanical test. Also, influence of nanoclay presence on water vapor permeability (WVP), color and transparency of the nanocomposites were investigated. Results & Discussion: The results showed that nanoclay addition improved the mechanical properties (Young’s modulus, elongation at break and tensile strength) and WVP up to 3% (wt). However, nanoclay addition reduced the transparency of resultant nanocomposites films but it prevented wave transmission at three UV region which leads to better protective effect of film as a food packaging materials. It seems that introduction of Cloisite 15A into the PET matrix reinforced the mechanical properties of resultant nanocomposites. The Young’s modulus of the nanocompo-sites significantly increased compared with the neat PET, indicating that PET/Cloisite 15A nanocomposites were stiffer than PET. The maximum Young’s modulus was observed for PET/C15A containing 3% wt with an increment about 8 MPa. This increase in modulus may be attributed to uniform dispersion and alignment of nanoclay along with compatibil-ity with PET matrix as confirmed by XRD, DSC and SEM. The Young’s modulus enhancement is consistent with that of other research (KIMet al. 2007; Scaffaroet al. 2011; Ghanbari et al. 2013a,b]. Tensile strength like elongation at break shows same trend, increases on increasing nanoclay content except for nanocomposite containing 5% which indicates brittle behavior compared to PET. This can be explained consider-ing that higher aspect ratio of nanoclay tends to aggregate and forms tactoids (as shown in SEM and XRD) and conse-quently indicates poor mechanical properties.
Saina Moayedzadeh; Asghar Khosrowshahi; Shahin Zomorodi
Abstract
Introduction: Microbil transglutaminase (MTG, E.C. 2.3.2.13) is a transferase enzyme that catalyses the acyl transfer reaction between -carboxyamide groups of peptide-bound glutamine residues and the primary amino groups including -amino groups of lysine residues. This will lead to the formation ...
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Introduction: Microbil transglutaminase (MTG, E.C. 2.3.2.13) is a transferase enzyme that catalyses the acyl transfer reaction between -carboxyamide groups of peptide-bound glutamine residues and the primary amino groups including -amino groups of lysine residues. This will lead to the formation of new intra- and intermolecular crosslinks between proteins in order to formation of polymers with high molecular weight. Such crosslinks can modify the structure and functionality of proteins. Actually, crosslinking of milk proteins caused by enzyme leads to improvement in functional characteristics of proteins and formation of products with desirable sensory and rheological properties. Nowadays enzymatic cross-linking is widely used to improve the functional properties of proteins. Because undesirable side reactions that could lead to produce of toxic co-products by chemical modification may be minimized by enzyme catalysis. In last twenty years, consumer trends towards low or non-fat dairy products especially nonfat yoghurt have increased because of harmful effects of excess fat on human health. However, many consumers prefer low-fat products with a similar sensory quality to full-fat ones. The traditional methods used to improve yoghurt texture and decrease syneresis include the enrichment of dry matter (total solids) and/or protein content, as well as the addition of natural or synthetic gums. The polymerization of milk protein chains by transglutaminase for three-dimensional net stabilization in yoghurt provides new technology to prevent common problems in dairy product processing. In this study, the effect of microbial transglutaminase concentration, incorporation amount of sodium caseinate into milk and storage time on proteolysis, rheological properties and water holding capacity of nonfat stirred yoghurt was investigated using response surface method (RSM). Materials and methods: Twenty treatments were carried out according to a face-central composite design with three factors and three levels for each variable. The independent variables of the design were Enzyme concentration, amount of sodium caseinate and storage time. They were in the range of 0-2 Unit per gram of milk protein, 0-1.27 percent and 1-19 days, respectively. For preparation of samples, first of all the SNF and protein content of milk were fortified by addition of skim milk powder and sodium caseinate. The milk was tempered to 50°C in a water bath and subsequently transglutaminase was added at different concentration. It was incubated for 1 hour at 50°C in the water bath. Then it was pasteurized at 85°C for 15 min to inactive the enzymatic reaction and cooled to 45°C. After inoculation with the appropriate inoculum type according to the commercial recommendation, incubated at 42°C until the pH value of 4.6 was obtained. The yogurt samples were cooled in ice-water bath and stirred for 60 second using manual stirrer. Samples were distributed into sterilized plastic containers; they were sealed and stored at 4°C until examined. Characteristics of all yoghurt samples were evaluated, such as: proteolysis by using o-pthaldialdehyde (OPA) assay, apparent viscosity by Brookfield viscometer and water holding capacity. Proteolysis was carried on 3 steps including preparation of yoghurt water extracts, preparation of OPA reagent and absorbance measurements. Briefly, 150 µl of yogurt serum was added directly to 3 ml of OPA reagent in a 5 mL quartz cuvette and the solutions were mixed briefly by inversion prior to 2 min incubation at room temperature followed by absorbance measurement at 340 nm.Results and discussion: The statistical analysis of results showed that increase in enzyme concentration increased viscosity and water holding capacity of samples and decreased the proteolysis (p≤0.05). The presence of transglutaminase contributed to an increase in the viscosity due to its ability to form high molecular weight polymers from protein monomers. Crosslinking of protein chains stabilized the three-dimensional network of yoghurt gel and prevented yoghurt whey expulsion as a result of a decrease in gel permeability; thus, increasing water holding capacity. The lesser proteolytic activity with using transglutaminase may be explained by a combination of these two factors: 1) transglutaminase-induced cross-linked milk proteins were less suitable substrates for proteolytic enzymes in starter culture than native milk proteins and, 2) Proteolytic products such as peptides were crosslinked into the milk proteins by transglutaminase. It is known that the yoghurt may become too acidic and bitter due to excessive acidification and proteolysis even at refrigerator temperatures. The development of these defects generally determines the shelf life. Our results indicate that it may be possible to produce yoghurts with longer shelf life when using transglutaminase. Addition of sodium caseinate resulted in the increased viscosity and water holding capacity of samples. Also, during the storage period, water holding capacity was decreased and proteolysis of samples was significantly increased (p≤0.05). Conclusion: The optimum conditions for the production of yoghurt was obtained using 1.42 Unit enzyme per gram of milk protein, 0.47 percent sodium caseinate with a storage period of 15 days. The overall desirability value was equal to 0.83. Under these conditions the predicted percentage of water holding capacity, viscosity and proteolysis being 27.51, 5220 cp and the absorbance at 340nm was 0.349 nm (as proteolysis index), respectively
Hadi Almasi; Babak Ghanbarzadeh; Jalal Dehghan nia; Ali Akbar Entezami; Asghar Khosrowshahi Asl
Abstract
Fatty acid modified cellulose nanofibers (MCNFs) and TBHQ antioxidant were added to poly(lactic acid) (PLA) film. The combined effects of the MCNFs and TBHQ on the morphological, thermal, mechanical and barrier properties of PLA film were analyzed. The morphology of fracture surfaces evaluated by field ...
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Fatty acid modified cellulose nanofibers (MCNFs) and TBHQ antioxidant were added to poly(lactic acid) (PLA) film. The combined effects of the MCNFs and TBHQ on the morphological, thermal, mechanical and barrier properties of PLA film were analyzed. The morphology of fracture surfaces evaluated by field emission scanning electron microscopy (FE-SEM). XRD results showed that the crystallinity of the PLA film with added MCNFs was substantially higher than that of pure PLA and antioxidant active PLA films. Glass transition and melting temperatures changed with the addition of these two components. The addition of 3wt% of TBHQ to PLA films leads to a significant reduction (p
Nasrin Faraji; Mohammad Alizadeh khaled abad; Asghar Khosrowshahi; Soheila Faraji
Abstract
Heart disease - cardiovascular, cancer and obesity are the main causes of death and there are direct relationship between the consumption of high-fat foods and the incidence of these diseases. Therefore the demand for low-fat food products and probiotics has been dramatically increased. In this study, ...
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Heart disease - cardiovascular, cancer and obesity are the main causes of death and there are direct relationship between the consumption of high-fat foods and the incidence of these diseases. Therefore the demand for low-fat food products and probiotics has been dramatically increased. In this study, the effect of different levels of three hydrocolloids (inulin, chitosan and xanthan) at three levels (1, 2 and 3%) on survival of Lactobacillus acidophilus, physicochemical and sensory properties of yogurt during 15 days of storage was explored using a combined design. Increased levels of inulin and chitosan positively affected La-5 count, apparent viscosity, acidity and sensory scores during storage. Using graphical method of optimizing (overlaid contour plots), optimum ratios were: inulin 93.4%, xanthan 0.6% and chitosan 6%.
Javad Hesari; Mohammad Reza Ehsani; Asghar Khosrowshahi; Nasser Ghaemi
Abstract
Abstract
The objective of this study was to determine the effect of psychrotrophic bacteria and somatic cells on the physicochemical characteristics of Iranian ultrafiltered (UF) white cheese. Milks with different numbers of psychrotrophic bacteria (1×106, 5×106 and 10×106 cfu/ml) and low somatic ...
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Abstract
The objective of this study was to determine the effect of psychrotrophic bacteria and somatic cells on the physicochemical characteristics of Iranian ultrafiltered (UF) white cheese. Milks with different numbers of psychrotrophic bacteria (1×106, 5×106 and 10×106 cfu/ml) and low somatic cell counts (SCC,
